1. Field of the Invention
The invention relates to package tying machines and more particularly relates to twine catchers and knife trap assemblies for package tying machines.
2. Description of the Prior Art
Tying machines for bundles and other packages are designed with minimal modification, to accommodate both natural fiber twine and synthetic tie materials. The twine is threaded from a twine cone through a rotatably twine arm, and then fastened to a twine catcher located below the tying machine's table adjacent the knotting mechanism thereof. During a tying cycle, the end of the twine is held by the twine catcher and the twine arm is accelerated almost instantly from a standstill to the rotational speed of the drive for the arm to wrap the twine about the bundle to be tied. An additional portion of the twine is then held by the twine catcher while the knot is being formed. It will be understood then that the twine catcher of the so-called stringholder assembly is the spring-biased button which holds the free or tail end of the twine during the wrapping cycle and while the knot is being formed, and which also retains the future second end of the twine after the wrapping cycle has been completed and while the knot is being formed.
For purposes of the present invention, familiarity with package tying machines is presumed and reference is made to U.S. Pat. No. 1,606,290 for a detailed description of the operational cooperation of the various component parts of a package tying machine; and to U.S. Pat. No. 3,708,190 for a detailed description of a dual-tension stringholder assembly for package tying machines. Reference is also directed to U.S. Pat. No. 2,274,525 -- over which patent the present invention is an improvement -- for a detailed description of the configuration of a typical stringholder assembly.
The problem of misties, i.e., incomplete or completely missed knots, has long plagued package tying machine operations. Oftentimes during the continuous use of a tying machine, peelings and chaff from the tie material -- whether the latter be cotton or synthetic twine, plastic tape, or other type material -- will build up behind the stringholder button to such an extent that the desired clamping action of the stringholder mechanism, and the resultant tensioning of the tie material, is greatly diminished. This in turn will result in misties or even sometimes allow the clamped end of the tie material to completely fall out.
The above-noted peeling buildup problem occurs primarily because the prior art stringholders are allowed to oscillate and pivot over, i.e., self-cam, to any of various offset clamping positions as the direction of pull of the tie material varies. Thus, the prior art stringholder buttons can desirably cant over -- while clamping down forcefully against the associated tie material and the bearing face of the stringholder's support structure -- in the direction that the tie material assumes during the completion of the tying machine's wrapping cycle. However, the button can also undesirably cant over in the direction the tie material assumes during the machine's knotting and pull out cycles and thereby effect excessive clamping forces tending to lock the tie material in place and thus to inhibit the last-mentioned cycles. This excessive clamping action also tends to strip off tie material filaments thereby causing chaff to build up which in turn increases the occurrence of misties, requires systematic stringholder clean up, and necessitates machine down time. For purposes of describing this invention, the specific tie material in question will be cotton twine. However, it is to be understood that any of the above-noted types of tie materials can be utilized.
Test experiments have shown that with prior art stringholders misties occur at the approximate rate of 1 mistie in every 100 tying cycles. However, utilization of the present invention has achieved test results of only 1 mistie per several thousand tying cycles for smaller diameter twines. One specific test ran through approximately 38,000 tying cycles before a mistie occurred.
Additionally, it is to be noted that misties can occur from what is termed premature pull out, i.e., when the clamped end of the twine is completely or partially pulled out of the stringholder before either the machine's wrapping or knotting cycles is completed. This problem is especially prevalent with the plastic tape type of tie materials. Such premature pull out can occur from either the above-noted chaff buildup with attendant diminished clamping power in the stringholder, or from the early severing and then partial pull out of the newly clamped twine end as the previously clamped twine end is properly dislodged by the action of the knife trap assembly; the latter action is discussed in detail later herein.
Another rather significant problem with prior art stringholder mechanisms is the fact that several different stringholder set-ups -- with different hand-filed configurations, surface finishes, and associated spring members -- were required to accommodate the various types, weights, and sizes of natural and synthetic tie materials being utilized by package tying machine users. In recent times, as many as thirty different stringholder mechanism set-ups were needed to handle the various tie materials. Utilization of the herein-disclosed invention, because of its advantageous ability to effectively clamp the twine in limited directions only, has dramatically reduced the requirement for different stringholders to some five basic set-ups.